In an apparatus for mass transfer between a liquid and a gas inside a rotor, liquid is supplied to the center of the rotor and is driven outward by the centrifugal force generated by rotation of the rotor and gas surrounding the rotor is forced inward through the rotor by the gas pressure, counter to the liquid flow in the rotor.
WO 2015/101826 (U.S. Pat. No. 9,987,589) and WO 2016/038480 (US 2017/0028311) disclose mass-transfer machines having a rotor that has two lateral faces, a packing that drives centrally delivered liquid outward as the rotor rotates in the space between the two faces. Here the rotor is surrounded by a gas that due to the gas pressure flows through the rotor counter to the liquid, in order to produce a mass transfer between the liquid and the gas.